Auto merge of #46550 - jseyfried:cleanup_builtin_hygiene, r=nrc

macros: hygienize use of `core`/`std` in builtin macros

Today, if a builtin macro wants to access an item from `core` or `std` (depending `#![no_std]`), it generates `::core::path::to::item` or `::std::path::to::item` respectively (c.f. `fn std_path()` in `libsyntax/ext/base.rs`).

This PR refactors the builtin macros to instead always emit `$crate::path::to::item` here. That is, the def site of builtin macros is taken to be in `extern crate core;` or `extern crate std;`. Since builtin macros are macros 1.0 (i.e. mostly unhygienic), changing the def site can only effect the resolution of `$crate`.

r? @nrc

1 files changed, 4 insertions, 3 deletions

diff --git a/src/libsyntax_ext/deriving/debug.rs b/src/libsyntax_ext/deriving/debug.rs
index ab6dd04520c..82fc09fca69 100644
--- a/src/libsyntax_ext/deriving/debug.rs
+++ b/src/libsyntax_ext/deriving/debug.rs
@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use deriving::path_std;
 use deriving::generic::*;
 use deriving::generic::ty::*;
 
@@ -24,13 +25,13 @@ pub fn expand_deriving_debug(cx: &mut ExtCtxt,
                              item: &Annotatable,
                              push: &mut FnMut(Annotatable)) {
     // &mut ::std::fmt::Formatter
-    let fmtr = Ptr(Box::new(Literal(path_std!(cx, core::fmt::Formatter))),
+    let fmtr = Ptr(Box::new(Literal(path_std!(cx, fmt::Formatter))),
                    Borrowed(None, ast::Mutability::Mutable));
 
     let trait_def = TraitDef {
         span,
         attributes: Vec::new(),
-        path: path_std!(cx, core::fmt::Debug),
+        path: path_std!(cx, fmt::Debug),
         additional_bounds: Vec::new(),
         generics: LifetimeBounds::empty(),
         is_unsafe: false,
@@ -40,7 +41,7 @@ pub fn expand_deriving_debug(cx: &mut ExtCtxt,
                           generics: LifetimeBounds::empty(),
                           explicit_self: borrowed_explicit_self(),
                           args: vec![fmtr],
-                          ret_ty: Literal(path_std!(cx, core::fmt::Result)),
+                          ret_ty: Literal(path_std!(cx, fmt::Result)),
                           attributes: Vec::new(),
                           is_unsafe: false,
                           unify_fieldless_variants: false,